1. Field of the Invention
The invention relates to offshore drilling and production operations and is specifically directed to marine drilling workover/intervention, and production riser slip-joint and tensioning devices and methodologies.
2. Description of Related Art
A marine riser system is employed to provide a conduit from a floating vessel at the water surface to the blowout preventer stack or, production tree, which is connected to the wellhead at the sea floor. A slip-joint is incorporated into the riser string to compensate for vessel motion induced by wave action and heave. A tensioning system is utilized to maintain a variable tension to the riser string alleviating the potential for compression and in turn buckling or failure.
Historically, conventional riser tensioner systems have consisted of both single and dual cylinder assemblies with a fixed cable sheave at one end of the cylinder and a movable cable sheave attached to the rod end of the cylinder. The assembly is then mounted in a position on the vessel to allow convenient routing of wire rope which is connected to a point at the fixed end and strung over the movable sheaves. In turn, the wire rope is routed via additional sheaves and connected to the slip-joint assembly via a support ring consisting of pad eyes which accept the end termination of the wire rope assembly. A hydro/pneumatic system consisting of high pressure air over hydraulic fluid applied to the cylinder forces the rod and in turn the rod end sheave to stroke out thereby tensioning the wire rope and in turn the riser.
The number of tensioner units employed is based on the tension necessary to maintain support of the riser and a percentage of overpull which is dictated by met-ocean conditions i.e., current and operational parameters including variable mud weight, etc.
Normal operation of these conventional type tensioning systems have required high maintenance due to the constant motion producing wear and degradation of the wire rope members. Replacing the active working sections of the wire rope by slipping and cutting raises safety concerns for personnel and has not proven cost effective. In addition, available space for installation and, the structure necessary to support the units including weight and loads imposed, particularly in deep water applications where the tension necessary requires additional tensioners poses difficult problems for system configurations for both new vessel designs and upgrading existing vessel designs.
Recent deepwater development commitments have created a need for new generation drilling vessels and production facilities requiring a plethora of new technologies and systems to operate effectively in deep water and alien/harsh environments. These new technologies include riser tensioner development where direct acting cylinders are utilized.
Current systems as manufactured by Hydralift employ individual cylinders arranged to connect one end to the underside of the vessel sub-structure and one end to the slip-joint outer barrel. These direct acting cylinders are equipped with ball joint assemblies in both the rod end and cylinder end to compensate for riser angle and vessel offset. Although this arrangement is an improvement over conventional wire rope systems, there are both operational and configuration problems associated with the application and vessel interface. For example, one problem is the occurrence of rod and seal failure due to the bending induced by unequal and non-linear loading caused by vessel roll and pitch. Additionally, these systems cannot slide off of the wellbore centerline to allow access to the well. For example, the crew on the oil drilling vessel is not able to access equipment on the seabed floor without having to remove and breakdown the riser string.
The integration of the slip-joint and tensioner system is an improvement over existing conventional and direct acting tensioning systems. Beyond the normal operational application to provide a means to apply variable tension to the marine riser, the system provides a number of enhancements and options including vessel configuration and its operational criteria.
The integrated slip-joint and tensioner system has a direct and positive impact on vessel application and operating parameters by extending the depth of the water in which the system may be used and operational capability. In particular, the system is adaptable to existing medium class vessels considered for upgrade by reducing the structure, space, top side weight and complexity in wire rope routing and maintenance, while at the same time increasing the number of operations which can be performed by a given vessel equipped with the integrated slip-joint and tensioner system.
Additionally, the present invention extends operational capabilities to deeper waters than conventional tensioners by permitting increased tension while reducing the size and height of the oil drilling vessel structure, reducing the amount of deck space required for the slip-joint and tensioner system, reducing the top-side weight, and increasing the oil drilling vessel""s stability by lowering its center of gravity.
Moreover, the tensioner/slip-joint module of the present invention is co-linearly symmetrical with tensioning cylinders and the slip-joint parallel to each other. Therefore, the present tensioner/slip-joint module eliminates offset and the resulting unequal loading that causes rapid rod and seal failure in some previous systems.
The tensioner/slip-joint module of the present invention is radially arranged and may be affixed to the oil drilling vessel at a single point. Therefore, the tensioner/slip-joint module may be conveniently installed or removed as a single unit through a rotary table opening, or disconnected and moved horizontally while still under the oil drilling vessel.
The tensioner/slip-joint module of the present invention further offers operational advantages over conventional methodologies by providing options in riser management and current well construction techniques. Applications of the basic module design are not limited to drilling risers and floating drilling vessels. The system further provides cost and operational effective solutions in well servicing/workover, intervention and production riser applications. These applications include all floating production facilities including, tension leg platform (T.L.P.) floating production facility (F.P.F.) and production spar variants. The system when installed provides an effective solution to tensioning requirements and operating parameters including improving safety by eliminating the need for personnel to slip and cut tensioner wires with the riser suspended in the vessel moon pool. An integral control and data acquisition system provides operating parameters to a central processor system which provides supervisory control.
The foregoing advantages have been obtained through the present tensioner/slip-joint module comprising: at least one mandrel; at least one upper flexjoint swivel assembly in communication with the at least one mandrel; at least one manifold in communication with the at least one upper flexjoint swivel assembly, the at least one manifold having a first radial fluid band and a second radial fluid band; at least one slip-joint assembly having an inner barrel slidably engaged within an outer barrel, the inner barrel having an inner barrel housing in communication with the at least one manifold; at least one tensioning cylinder having a blind end, a rod end, and at least one transfer tubing, the blind end being in communication with the first radial fluid band, the at least one transfer tubing being in communication with the second radial fluid band and the rod end being in communication with at least one flexjoint bearing; and a base in communication with the at least one flexjoint bearing.
An additional feature of the tensioner/slip-joint module is that tensioner/slip-joint module may further include at least one lower flexjoint swivel assembly in communication with the outer barrel and the base. A further feature of the tensioner/slip-joint module is that the manifold may include a third radial fluid band, the third radial fluid band being in communication with either the blind end or the at least one transfer tubing. Another feature of the tensioner/slip-joint module is that the first and third radial fluid bands may be in communication with the at least one transfer tubing and the second radial fluid band may be in communication with the blind end of the at least one tensioning cylinder. An additional feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include six tensioning cylinders, wherein at least one tensioning cylinder may be in communication with a first control source and at least one tensioning cylinder may be in communication with a second control source. Still another feature of the tensioner/slip joint module is that the first control source and second control source may be in communication with the same tensioning cylinder. A further feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include a hang off donut. Another feature of the tensioner/slip-joint module is that the hang off donut may be disposed on the mandrel or along the tensioning cylinders, e.g., below the blind end of the tensioning cylinders which captures each of the tensioning cylinders and allows for the transference of axial tension load from the cylinder casing to the mandrel and then directly to the rig structure. An additional feature of the tensioner/slip-joint module is that the blind end may be connected to the manifold by at least one sub seal. Still another feature of the tensioner/slip-joint module is that each of the at least one tensioning cylinder may include at least one cylinderhead. Yet another feature of the tensioner/slip-joint module is that the first, second, and third radial fluid bands may each be in communication with a transducer. A further feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include at least two tensioning cylinders. Another feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include two radial fluid bands in communication with at least one transfer tubing and one radial fluid band in communication with the blind end of each of the at least one tensioning cylinder. An additional feature of the tensioner/slip-joint module is that a sub-manifold may be included between the blind end of the tensioning cylinder and the manifold, thereby permitting remotely operated valves to be disposed in the communication channels between the tensioning cylinders and the manifold making it possible to isolate any single or combination of tensioning cylinders for operation, maintenance and Riser Disconnect Management Systems (RDMS) procedures. Still another feature of the tensioner/slip-joint module is that a swivel feature may be incorporated either within or in the area of the manifold or upper flexjoint swivel assembly, thereby providing a means to remotely turn the entire tensioner/slip-joint module to remove torsional stresses in the riser string that result from the vessel changing heading. A further feature of the tensioner/slip-joint module is that the slip-joint assembly may be inverted with the inner barrel located below the outer barrel.
The foregoing advantages have also been achieved through the present tensioner/slip-joint comprising: at least one mandrel having a first mandrel end and a second mandrel end; at least one upper flexjoint swivel assembly having a first upper flexjoint swivel assembly end and a second upper flexjoint swivel assembly end; at least one manifold having a first manifold surface and a second manifold surface; at least one slip-joint assembly having a first slip-joint assembly end and a second slip-joint assembly end; at least one tensioning cylinder having a blind end, a rod end, and at least one flexjoint bearing in communication with the rod end; and a base, wherein the second mandrel end is connected to the first upper flexjoint swivel assembly end, the second upper flexjoint swivel assembly end is connected to the first manifold surface, the second manifold surface is connected to the first slip-joint assembly end and the blind end, the second slip-joint assembly end and the at least one flexjoint bearing are connected to the base.
An additional feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may further include at least one lower flexjoint swivel assembly having a first lower flexjoint swivel assembly end and a second lower flexjoint swivel assembly end, wherein the second slip-joint assembly end is connected to the first lower flexjoint swivel assembly end, and the at least one flexjoint bearing and the second lower flexjoint swivel assembly end are connected to the base. A further feature of the tensioner/slip-joint module is that the at least one tensioning cylinder may include at least one transfer tubing, the at least one transfer tubing being in communication with the manifold. Another feature of the tensioner/slip-joint module is that the manifold may include two radial fluid bands in communication with the at least one transfer tubing and one radial fluid band in communication with the blind end of the at least one tensioning cylinder. An additional feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include six tensioning cylinders, wherein at least one of the tensioning cylinders is in communication with a first control source and at least one tensioning cylinder is in communication with a second control source. Still another feature of the tensioner/slip-joint module is that the first control source and the second control source may be in communication with the same tensioning cylinder. A further feature of the tensioner/slip-joint module is that the tensioner/slip-joint module may include a hang off donut. Another feature of the tensioner/slip-joint module is that the slip-joint assembly may include an inner barrel slidably engaged within an outer barrel. An additional feature of the tensioner/slip-joint module is that the at least one manifold may include at least two radial fluid bands.
The foregoing advantages have also been achieved through the present tensioner/slip-joint module comprising: at least one mandrel, at least one upper flexjoint swivel assembly, at least one manifold, at least one slip-joint assembly, and at least one tensioning cylinder, wherein the at least one mandrel, the at least one upper flexjoint swivel assembly, the at least one manifold, the at least one slipjoint assembly, and the at least one tensioning cylinder are integral forming a unitary, co-linear tensioner/slip-joint module.
A further feature of the tensioner/slip-joint module is that the tensioner/slip-joint assembly further includes at least one lower flexjoint swivel assembly. An additional feature of the tensioner/slip-joint assembly is that the at least one mandrel may be connected to the at least one upper flexjoint swivel assembly, the at least one upper flexjoint swivel assembly may be connected to the at least one manifold, the at least one manifold may be connected to the at least one slip-joint assembly and the at least one tensioning cylinder, and the at least one slip-joint assembly and the at least one tensioning cylinder may be connected to the at least one lower flexjoint swivel assembly.
The foregoing advantages have also been achieved through the present method of compensating for offset of an oil drilling vessel connected to a riser or blowout preventer stack comprising the steps of: providing a tensioner/slip-joint module, the tensioner/slip-joint module having at least one mandrel, at least one upper flexjoint swivel assembly, at least one manifold, at least one slip-joint assembly, and at least one tensioning cylinder, wherein the at least one mandrel, the at least one upper flexjoint swivel assembly, the at least one manifold, the at least one slip-joint assembly, and the at least one tensioning cylinder are assembled to form a unitary, co-linear tensioner/slip-joint module; placing the tensioner/slip-joint module in communication with the oil drilling vessel and the riser or blowout preventer stack; and placing the manifold in communication with at least one control source.